This invention has to do with saw blades. More particularly, the invention is concerned with an improvement in saw blades comprising a variation progressively in the rake angle of the teeth from negative to positive to enable faster initiation of the stroke on the one hand, and greater cutting albeit with greater resistence at the terminal end of a stroke whereby cutting effort is maintained relatively constant over a saw stroke.
In general, the invention pertains to blades employable in hand saws which are operated in a reciprocating manner. The blades for such saws are generally made with a negative rake, that is, the cutting surface of the tooth is slanted back for smooth cutting. A positive rake, one in which the cutting surface of the tooth is slanted forward is best adapted for rapid cutting. In general, the negative rake angle of a tooth is used for workpiece cutting cross-cut saws, the positive rake is used for rip-sawing wood or cutting very homogeneous materials. A positive rake is also advantageous in saws used for pruning, tree trimming and the sawing of wet wood.
Having a negative rake angle on the tooth enables a cross-cut saw to start easily and cut smoothly, but cutting efficiency is relatively poor. On the other hand, a positive rake angle tooth such as is provided in a rip-saw cuts very efficiently, but it is difficult to start a stroke and the teeth tend to stick in the kerf since the teeth tend to dig in to the workpiece at the initiation of the stroke. Such sticking causes buckling of the blades particularly in thin, push saws like keyhole saws, and in some instances tends to snap the blades in tension, on small pull saws like coping saws and jeweler's saws.
In presently known pruning saws of the pull type snagging of teeth is reduced by curving the blade so that the initial part of the stroke has reduced engagement force, nonetheless snagging is still present to a degree, and caused by the self-engagement tendency of the positive rake angle teeth of the saw.